1. Field of the Invention
The invention concerns a radiant heating body for a cooking hob, in particular a glass ceramic cooking hob, having a heating conductor comprising a metal foil and an insulating bottom under the heating conductor, wherein the heating conductor extends in a geometrical pattern between the cooking hob and the insulating bottom.
2. Discussion of the Prior Art
A radiant heating body of that kind is described in DE 42 29 375 A1 and EP 0 585 831 A2. The heating conductor comprises a flexible flat strip which is laid in a spiral configuration on the insulating bottom in such a way that its large surface is perpendicular to the insulating bottom and to the cooking hob. Only its narrow upper edge is towards the cooking hob. By virtue of that arrangement the large surfaces radiate heat to each other.
For the purposes of fixing the heating conductor strip in position it has at its lower edge holding plate portions or tongues which are fitted into the insulating bottom itself. Assembly of the heating conductor is a complicated and expensive operation as the flat strip must be laid in spiral-shaped turns and the holding tongues have to be pressed into the insulating bottom.
At the high temperatures, greater than 600.degree. C., involved in radiant operation, corresponding expansion phenomena at the heating conductor occur, which may not result in the heating conductor coming loose from the insulating bottom.
EP 0 175 662 B1 describes a heating conductor whose flat geometrical pattern is separated by stamping out of a foil laminate including a metal foil. That heating body is only suitable for temperatures below 200.degree. C., a maximum of 400.degree. C., and cannot therefore be used as a radiant heating body.
EP 0 175 662 B1 provides for stamping out of the foil laminate two heating bodies in metal form, which are in mutually internested relationship, which reduces the amount of stamping wastage.
EP 0 229 928 A2 discloses a heating element for cooking units, which has a heating conductor path using flat conductor technology, preferably thick-film paste technology, which is applied to a carrier element which is stable in respect of shape. That publication does not describe a radiant heating body in which glowing operation of the heating conductor path is an important consideration.
U.S. Pat. No. 3,567,906 describes a flat heating wire which is wound in a sinusoidal configuration and which is laid in parallel strips beneath the cooking surface. The flat heating wire is not to be visible through the cooking surface. This therefore does not involve a radiant heating body in which it is important for the heating conductor to glow visibly for the user.
DE 41 22 106 A1 discloses a radiant heating body whose heating turns are held down on the insulating bottom by means of a shaped member.